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<div class="section">
<div class="titlepage"><div><div><h3 class="title">
<a name="boost_asio.reference.basic_waitable_timer"></a><a class="link" href="basic_waitable_timer.html" title="basic_waitable_timer">basic_waitable_timer</a>
</h3></div></div></div>
<p>
        <a class="indexterm" name="boost_asio.indexterm.basic_waitable_timer"></a>
      </p>
<p>
        Provides waitable timer functionality.
      </p>
<pre class="programlisting"><span class="keyword">template</span><span class="special">&lt;</span>
    <span class="keyword">typename</span> <span class="identifier">Clock</span><span class="special">,</span>
    <span class="keyword">typename</span> <a class="link" href="WaitTraits.html" title="Wait traits requirements">WaitTraits</a><span class="special">,</span>
    <span class="keyword">typename</span> <a class="link" href="Executor1.html" title="Executor requirements">Executor</a><span class="special">&gt;</span>
<span class="keyword">class</span> <span class="identifier">basic_waitable_timer</span>
</pre>
<h5>
<a name="boost_asio.reference.basic_waitable_timer.h0"></a>
        <span class="phrase"><a name="boost_asio.reference.basic_waitable_timer.types"></a></span><a class="link" href="basic_waitable_timer.html#boost_asio.reference.basic_waitable_timer.types">Types</a>
      </h5>
<div class="informaltable"><table class="table">
<colgroup>
<col>
<col>
</colgroup>
<thead><tr>
<th>
                <p>
                  Name
                </p>
              </th>
<th>
                <p>
                  Description
                </p>
              </th>
</tr></thead>
<tbody>
<tr>
<td>
                <p>
                  <a class="link" href="basic_waitable_timer__rebind_executor.html" title="basic_waitable_timer::rebind_executor"><span class="bold"><strong>rebind_executor</strong></span></a>
                </p>
              </td>
<td>
                <p>
                  Rebinds the timer type to another executor.
                </p>
              </td>
</tr>
<tr>
<td>
                <p>
                  <a class="link" href="basic_waitable_timer/clock_type.html" title="basic_waitable_timer::clock_type"><span class="bold"><strong>clock_type</strong></span></a>
                </p>
              </td>
<td>
                <p>
                  The clock type.
                </p>
              </td>
</tr>
<tr>
<td>
                <p>
                  <a class="link" href="basic_waitable_timer/duration.html" title="basic_waitable_timer::duration"><span class="bold"><strong>duration</strong></span></a>
                </p>
              </td>
<td>
                <p>
                  The duration type of the clock.
                </p>
              </td>
</tr>
<tr>
<td>
                <p>
                  <a class="link" href="basic_waitable_timer/executor_type.html" title="basic_waitable_timer::executor_type"><span class="bold"><strong>executor_type</strong></span></a>
                </p>
              </td>
<td>
                <p>
                  The type of the executor associated with the object.
                </p>
              </td>
</tr>
<tr>
<td>
                <p>
                  <a class="link" href="basic_waitable_timer/time_point.html" title="basic_waitable_timer::time_point"><span class="bold"><strong>time_point</strong></span></a>
                </p>
              </td>
<td>
                <p>
                  The time point type of the clock.
                </p>
              </td>
</tr>
<tr>
<td>
                <p>
                  <a class="link" href="basic_waitable_timer/traits_type.html" title="basic_waitable_timer::traits_type"><span class="bold"><strong>traits_type</strong></span></a>
                </p>
              </td>
<td>
                <p>
                  The wait traits type.
                </p>
              </td>
</tr>
</tbody>
</table></div>
<h5>
<a name="boost_asio.reference.basic_waitable_timer.h1"></a>
        <span class="phrase"><a name="boost_asio.reference.basic_waitable_timer.member_functions"></a></span><a class="link" href="basic_waitable_timer.html#boost_asio.reference.basic_waitable_timer.member_functions">Member
        Functions</a>
      </h5>
<div class="informaltable"><table class="table">
<colgroup>
<col>
<col>
</colgroup>
<thead><tr>
<th>
                <p>
                  Name
                </p>
              </th>
<th>
                <p>
                  Description
                </p>
              </th>
</tr></thead>
<tbody>
<tr>
<td>
                <p>
                  <a class="link" href="basic_waitable_timer/async_wait.html" title="basic_waitable_timer::async_wait"><span class="bold"><strong>async_wait</strong></span></a>
                </p>
              </td>
<td>
                <p>
                  Start an asynchronous wait on the timer.
                </p>
              </td>
</tr>
<tr>
<td>
                <p>
                  <a class="link" href="basic_waitable_timer/basic_waitable_timer.html" title="basic_waitable_timer::basic_waitable_timer"><span class="bold"><strong>basic_waitable_timer</strong></span></a> <span class="silver">[constructor]</span>
                </p>
              </td>
<td>
                <p>
                  Constructor. <br> <span class="silver"> —</span><br> Constructor to set a particular expiry
                  time as an absolute time. <br> <span class="silver"> —</span><br> Constructor to set a particular
                  expiry time relative to now. <br> <span class="silver"> —</span><br> Move-construct a basic_waitable_timer
                  from another.
                </p>
              </td>
</tr>
<tr>
<td>
                <p>
                  <a class="link" href="basic_waitable_timer/cancel.html" title="basic_waitable_timer::cancel"><span class="bold"><strong>cancel</strong></span></a>
                </p>
              </td>
<td>
                <p>
                  Cancel any asynchronous operations that are waiting on the timer.
                  <br> <span class="silver"> —</span><br> (Deprecated: Use non-error_code overload.) Cancel
                  any asynchronous operations that are waiting on the timer.
                </p>
              </td>
</tr>
<tr>
<td>
                <p>
                  <a class="link" href="basic_waitable_timer/cancel_one.html" title="basic_waitable_timer::cancel_one"><span class="bold"><strong>cancel_one</strong></span></a>
                </p>
              </td>
<td>
                <p>
                  Cancels one asynchronous operation that is waiting on the timer.
                  <br> <span class="silver"> —</span><br> (Deprecated: Use non-error_code overload.) Cancels
                  one asynchronous operation that is waiting on the timer.
                </p>
              </td>
</tr>
<tr>
<td>
                <p>
                  <a class="link" href="basic_waitable_timer/expires_after.html" title="basic_waitable_timer::expires_after"><span class="bold"><strong>expires_after</strong></span></a>
                </p>
              </td>
<td>
                <p>
                  Set the timer's expiry time relative to now.
                </p>
              </td>
</tr>
<tr>
<td>
                <p>
                  <a class="link" href="basic_waitable_timer/expires_at.html" title="basic_waitable_timer::expires_at"><span class="bold"><strong>expires_at</strong></span></a>
                </p>
              </td>
<td>
                <p>
                  (Deprecated: Use expiry().) Get the timer's expiry time as an absolute
                  time. <br> <span class="silver"> —</span><br> Set the timer's expiry time as an absolute
                  time. <br> <span class="silver"> —</span><br> (Deprecated: Use non-error_code overload.)
                  Set the timer's expiry time as an absolute time.
                </p>
              </td>
</tr>
<tr>
<td>
                <p>
                  <a class="link" href="basic_waitable_timer/expires_from_now.html" title="basic_waitable_timer::expires_from_now"><span class="bold"><strong>expires_from_now</strong></span></a>
                </p>
              </td>
<td>
                <p>
                  (Deprecated: Use expiry().) Get the timer's expiry time relative
                  to now. <br> <span class="silver"> —</span><br> (Deprecated: Use expires_after().) Set the
                  timer's expiry time relative to now.
                </p>
              </td>
</tr>
<tr>
<td>
                <p>
                  <a class="link" href="basic_waitable_timer/expiry.html" title="basic_waitable_timer::expiry"><span class="bold"><strong>expiry</strong></span></a>
                </p>
              </td>
<td>
                <p>
                  Get the timer's expiry time as an absolute time.
                </p>
              </td>
</tr>
<tr>
<td>
                <p>
                  <a class="link" href="basic_waitable_timer/get_executor.html" title="basic_waitable_timer::get_executor"><span class="bold"><strong>get_executor</strong></span></a>
                </p>
              </td>
<td>
                <p>
                  Get the executor associated with the object.
                </p>
              </td>
</tr>
<tr>
<td>
                <p>
                  <a class="link" href="basic_waitable_timer/operator_eq_.html" title="basic_waitable_timer::operator="><span class="bold"><strong>operator=</strong></span></a>
                </p>
              </td>
<td>
                <p>
                  Move-assign a basic_waitable_timer from another.
                </p>
              </td>
</tr>
<tr>
<td>
                <p>
                  <a class="link" href="basic_waitable_timer/wait.html" title="basic_waitable_timer::wait"><span class="bold"><strong>wait</strong></span></a>
                </p>
              </td>
<td>
                <p>
                  Perform a blocking wait on the timer.
                </p>
              </td>
</tr>
<tr>
<td>
                <p>
                  <a class="link" href="basic_waitable_timer/_basic_waitable_timer.html" title="basic_waitable_timer::~basic_waitable_timer"><span class="bold"><strong>~basic_waitable_timer</strong></span></a> <span class="silver">[destructor]</span>
                </p>
              </td>
<td>
                <p>
                  Destroys the timer.
                </p>
              </td>
</tr>
</tbody>
</table></div>
<p>
        The <a class="link" href="basic_waitable_timer.html" title="basic_waitable_timer"><code class="computeroutput"><span class="identifier">basic_waitable_timer</span></code></a> class template
        provides the ability to perform a blocking or asynchronous wait for a timer
        to expire.
      </p>
<p>
        A waitable timer is always in one of two states: "expired" or "not
        expired". If the <code class="computeroutput"><span class="identifier">wait</span><span class="special">()</span></code> or <code class="computeroutput"><span class="identifier">async_wait</span><span class="special">()</span></code> function is called on an expired timer,
        the wait operation will complete immediately.
      </p>
<p>
        Most applications will use one of the <a class="link" href="steady_timer.html" title="steady_timer"><code class="computeroutput"><span class="identifier">steady_timer</span></code></a>, <a class="link" href="system_timer.html" title="system_timer"><code class="computeroutput"><span class="identifier">system_timer</span></code></a> or <a class="link" href="high_resolution_timer.html" title="high_resolution_timer"><code class="computeroutput"><span class="identifier">high_resolution_timer</span></code></a> typedefs.
      </p>
<h5>
<a name="boost_asio.reference.basic_waitable_timer.h2"></a>
        <span class="phrase"><a name="boost_asio.reference.basic_waitable_timer.remarks"></a></span><a class="link" href="basic_waitable_timer.html#boost_asio.reference.basic_waitable_timer.remarks">Remarks</a>
      </h5>
<p>
        This waitable timer functionality is for use with the C++11 standard library's
        <code class="computeroutput"><span class="special">&lt;</span><span class="identifier">chrono</span><span class="special">&gt;</span></code> facility, or with the Boost.Chrono library.
      </p>
<h5>
<a name="boost_asio.reference.basic_waitable_timer.h3"></a>
        <span class="phrase"><a name="boost_asio.reference.basic_waitable_timer.thread_safety"></a></span><a class="link" href="basic_waitable_timer.html#boost_asio.reference.basic_waitable_timer.thread_safety">Thread
        Safety</a>
      </h5>
<p>
        <span class="emphasis"><em>Distinct</em></span> <span class="emphasis"><em>objects:</em></span> Safe.
      </p>
<p>
        <span class="emphasis"><em>Shared</em></span> <span class="emphasis"><em>objects:</em></span> Unsafe.
      </p>
<h5>
<a name="boost_asio.reference.basic_waitable_timer.h4"></a>
        <span class="phrase"><a name="boost_asio.reference.basic_waitable_timer.examples"></a></span><a class="link" href="basic_waitable_timer.html#boost_asio.reference.basic_waitable_timer.examples">Examples</a>
      </h5>
<p>
        Performing a blocking wait (C++11):
      </p>
<pre class="programlisting"><span class="comment">// Construct a timer without setting an expiry time.</span>
<span class="identifier">boost</span><span class="special">::</span><span class="identifier">asio</span><span class="special">::</span><span class="identifier">steady_timer</span> <span class="identifier">timer</span><span class="special">(</span><span class="identifier">my_context</span><span class="special">);</span>

<span class="comment">// Set an expiry time relative to now.</span>
<span class="identifier">timer</span><span class="special">.</span><span class="identifier">expires_after</span><span class="special">(</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">chrono</span><span class="special">::</span><span class="identifier">seconds</span><span class="special">(</span><span class="number">5</span><span class="special">));</span>

<span class="comment">// Wait for the timer to expire.</span>
<span class="identifier">timer</span><span class="special">.</span><span class="identifier">wait</span><span class="special">();</span>
</pre>
<p>
        Performing an asynchronous wait (C++11):
      </p>
<pre class="programlisting"><span class="keyword">void</span> <span class="identifier">handler</span><span class="special">(</span><span class="keyword">const</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">system</span><span class="special">::</span><span class="identifier">error_code</span><span class="special">&amp;</span> <span class="identifier">error</span><span class="special">)</span>
<span class="special">{</span>
  <span class="keyword">if</span> <span class="special">(!</span><span class="identifier">error</span><span class="special">)</span>
  <span class="special">{</span>
    <span class="comment">// Timer expired.</span>
  <span class="special">}</span>
<span class="special">}</span>

<span class="special">...</span>

<span class="comment">// Construct a timer with an absolute expiry time.</span>
<span class="identifier">boost</span><span class="special">::</span><span class="identifier">asio</span><span class="special">::</span><span class="identifier">steady_timer</span> <span class="identifier">timer</span><span class="special">(</span><span class="identifier">my_context</span><span class="special">,</span>
    <span class="identifier">std</span><span class="special">::</span><span class="identifier">chrono</span><span class="special">::</span><span class="identifier">steady_clock</span><span class="special">::</span><span class="identifier">now</span><span class="special">()</span> <span class="special">+</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">chrono</span><span class="special">::</span><span class="identifier">seconds</span><span class="special">(</span><span class="number">60</span><span class="special">));</span>

<span class="comment">// Start an asynchronous wait.</span>
<span class="identifier">timer</span><span class="special">.</span><span class="identifier">async_wait</span><span class="special">(</span><span class="identifier">handler</span><span class="special">);</span>
</pre>
<h5>
<a name="boost_asio.reference.basic_waitable_timer.h5"></a>
        <span class="phrase"><a name="boost_asio.reference.basic_waitable_timer.changing_an_active_waitable_timer_s_expiry_time"></a></span><a class="link" href="basic_waitable_timer.html#boost_asio.reference.basic_waitable_timer.changing_an_active_waitable_timer_s_expiry_time">Changing
        an active waitable timer's expiry time</a>
      </h5>
<p>
        Changing the expiry time of a timer while there are pending asynchronous
        waits causes those wait operations to be cancelled. To ensure that the action
        associated with the timer is performed only once, use something like this:
        used:
      </p>
<pre class="programlisting"><span class="keyword">void</span> <span class="identifier">on_some_event</span><span class="special">()</span>
<span class="special">{</span>
  <span class="keyword">if</span> <span class="special">(</span><span class="identifier">my_timer</span><span class="special">.</span><span class="identifier">expires_after</span><span class="special">(</span><span class="identifier">seconds</span><span class="special">(</span><span class="number">5</span><span class="special">))</span> <span class="special">&gt;</span> <span class="number">0</span><span class="special">)</span>
  <span class="special">{</span>
    <span class="comment">// We managed to cancel the timer. Start new asynchronous wait.</span>
    <span class="identifier">my_timer</span><span class="special">.</span><span class="identifier">async_wait</span><span class="special">(</span><span class="identifier">on_timeout</span><span class="special">);</span>
  <span class="special">}</span>
  <span class="keyword">else</span>
  <span class="special">{</span>
    <span class="comment">// Too late, timer has already expired!</span>
  <span class="special">}</span>
<span class="special">}</span>

<span class="keyword">void</span> <span class="identifier">on_timeout</span><span class="special">(</span><span class="keyword">const</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">system</span><span class="special">::</span><span class="identifier">error_code</span><span class="special">&amp;</span> <span class="identifier">e</span><span class="special">)</span>
<span class="special">{</span>
  <span class="keyword">if</span> <span class="special">(</span><span class="identifier">e</span> <span class="special">!=</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">asio</span><span class="special">::</span><span class="identifier">error</span><span class="special">::</span><span class="identifier">operation_aborted</span><span class="special">)</span>
  <span class="special">{</span>
    <span class="comment">// Timer was not cancelled, take necessary action.</span>
  <span class="special">}</span>
<span class="special">}</span>
</pre>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
            The <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">asio</span><span class="special">::</span><span class="identifier">basic_waitable_timer</span><span class="special">::</span><span class="identifier">expires_after</span><span class="special">()</span></code>
            function cancels any pending asynchronous waits, and returns the number
            of asynchronous waits that were cancelled. If it returns 0 then you were
            too late and the wait handler has already been executed, or will soon
            be executed. If it returns 1 then the wait handler was successfully cancelled.
          </li>
<li class="listitem">
            If a wait handler is cancelled, the boost::system::error_code passed
            to it contains the value <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">asio</span><span class="special">::</span><span class="identifier">error</span><span class="special">::</span><span class="identifier">operation_aborted</span></code>.
          </li>
</ul></div>
<h5>
<a name="boost_asio.reference.basic_waitable_timer.h6"></a>
        <span class="phrase"><a name="boost_asio.reference.basic_waitable_timer.requirements"></a></span><a class="link" href="basic_waitable_timer.html#boost_asio.reference.basic_waitable_timer.requirements">Requirements</a>
      </h5>
<p>
        <span class="emphasis"><em>Header: </em></span><code class="literal">boost/asio/basic_waitable_timer.hpp</code>
      </p>
<p>
        <span class="emphasis"><em>Convenience header: </em></span><code class="literal">boost/asio.hpp</code>
      </p>
</div>
<div class="copyright-footer">Copyright © 2003-2024 Christopher M. Kohlhoff<p>
        Distributed under the Boost Software License, Version 1.0. (See accompanying
        file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
      </p>
</div>
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